Ionic Compound Formulas www.lab-initio.com

Ions Cation: A positive ion Mg2+, NH4+ Anion: A negative ion Cl-, SO42-

Oxidation Number the total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom.

Predicting Ionic Charges Group 1: Lose 1 electron to form 1+ ions H+ Li+ Na+ K+

Predicting Ionic Charges Group 2: Loses 2 electrons to form 2+ ions Be2+ Mg2+ Ca2+ Sr2+ Ba2+

Predicting Ionic Charges Loses 3 electrons to form 3+ ions Group 13: B3+ Al3+ Ga3+

Predicting Ionic Charges Lose 4 electrons or gain 4 electrons? Group 14: Neither! Group 13 elements rarely form ions*** few exceptions

Predicting Ionic Charges Nitride Gains 3 electrons to form 3- ions Group 15: Phosphide P3- As3- Arsenide

Predicting Ionic Charges Oxide Gains 2 electrons to form 2- ions Group 16: S2- Sulfide Se2- Selenide

Predicting Ionic Charges Group 17: Gains 1 electron to form 1- ions F1- Fluoride Cl1- Chloride Br1- Bromide I1- Iodide

Predicting Ionic Charges Group 18: Stable Noble gases do not form ions!

Predicting Ionic Charges Many transition elements have more than one possible oxidation state. Groups 3 - 12: Iron(II) = Fe2+ Iron(III) = Fe3+

Predicting Ionic Charges Some transition elements have only one possible oxidation state. Groups 3 - 12: Zinc = Zn2+ Silver = Ag+

Elements that form Ions Metals usually form cations while Nonmetals usually form anions

Writing Ionic Compound Formulas Example: Barium nitrate 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Ba2+ ( ) NO3- 2 Not balanced!

Writing Ionic Compound Formulas Example: Ammonium sulfate 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. ( ) NH4+ SO42- 2 Not balanced!

Writing Ionic Compound Formulas Example: Iron(III) chloride 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Fe3+ Cl- 3 Not balanced!

Writing Ionic Compound Formulas Example: Aluminum sulfide 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Al3+ S2- 2 3 Not balanced!

Writing Ionic Compound Formulas Example: Magnesium carbonate 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. Mg2+ CO32- They are balanced!

Writing Ionic Compound Formulas Example: Zinc hydroxide 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. ( ) Zn2+ OH- 2 Not balanced!

Writing Ionic Compound Formulas Example: Aluminum phosphate 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. Al3+ PO43- They ARE balanced!

Example: Aluminum Chloride Criss-Cross Rule Example: Aluminum Chloride Aluminum Chloride Step 1: write out name with space Al Cl 3+ 1- Step 2: write symbols & charge of elements Al Cl Step 3: 1 3 http://upload.wikimedia.org/wikipedia/commons/4/42/Aluminium-trichloride-3D-structures.png criss-cross charges as subsrcipts Step 4: AlCl 3 combine as formula unit (“1” is never shown)

Example: Aluminum Chloride Criss-Cross Rule Example: Aluminum Chloride Step 1: Aluminum Chloride Step 2: Al3+ Cl1- Step 3: Al Cl 1 3 Step 4: AlCl 3

Example: Aluminum Oxide Criss-Cross Rule Example: Aluminum Oxide Step 1: Aluminum Oxide Step 2: Al3+ O2- Step 3: Al O 2 3 Step 4: Al2O3

Example: Magnesium Oxide Criss-Cross Rule Example: Magnesium Oxide Step 1: Magnesium Oxide Step 2: Mg2+ O2- Step 3: Mg O 2 2 Step 4: Mg2O2 Step 5: MgO

Naming Ionic Compounds Cation first, then anion Monatomic cation = name of the element Ca2+ = calcium ion Monatomic anion = root + -ide Cl- = chloride CaCl2 = calcium chloride

Multiple Charge Cations Ion Stock System Traditional System Fe 3+ iron (III) ferric Fe 2+ iron (II) ferrous Cu 2+ copper (II) cupric Cu 1+ copper (I) cuprous Co 3+ cobalt (III) cobaltic Co 2+ cobalt (II) cobaltous Sn 4+ tin (IV) stannic Sn 2+ tin (II) stannous Pb 4+ lead (IV) plumbic Pb 2+ lead (II) plumbous Hg 2+ mercury (II) mercuric Hg2 2+ mercury (I) mercurous *Mercury (I) ions are always bound together in pairs to form Hg2 2+ Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 90

Naming Ionic Compounds Metals with multiple oxidation states some metal forms more than one cation use Roman numeral in name PbCl2 Pb2+ is cation PbCl2 = lead(II) chloride

Naming Binary Compounds Formula Name barium oxide BaO ____________________ ________________ sodium bromide MgI2 ____________________ KCl ____________________ ________________ strontium fluoride ________________ cesium fluoride NaBr magnesium iodide potassium chloride SrF2 CsF